Solid laser excitation module

ABSTRACT

A solid state laser pumping module ( 1 ) is so constructed as to have a plate-shaped non-doped medium ( 4 ) having a refractive index close to that of a thin solid state laser medium ( 3 ) and having no active material, the non-doped medium being disposed on a surface of the thin solid state laser medium ( 3 ) which is opposite to a reflecting surface of the thin solid state laser medium ( 3 ). Pumping light is reflected between the reflecting surface of the thin solid state laser medium ( 3 ) and a reflecting surface of the non-doped medium ( 4 ) arranged on a side of the opposite surface of the thin solid state laser medium ( 3 ) while pumping the thin solid state laser medium ( 3 ). A laser beam is taken out of the thin solid state laser medium.

FIELD OF THE INVENTION

The present invention relates to a solid state laser pumping module thatuses a thin solid state laser medium.

BACKGROUND OF THE INVENTION

Conventionally, there has been provided a solid state laser pumpingmodule that is so constructed as to pump a thin solid state lasermedium. Such a solid state laser pumping module has a pumping sourcearranged opposite to a thin plate which is a solid state laser medium,and is so constructed as to pump this thin solid state laser medium.Such a technology is disclosed in, for example, U.S. Pat. No. 5,553,088,by Braichet al., on Sep. 3, 1996.

The related art solid state laser pumping module using the thin solidstate laser medium needs to enlarge side surfaces of the thin solidstate laser medium which are pumping surfaces in order to raise theproportion of pumping light incident upon the side surfaces because itis so constructed as to receive pumping light from the side surfaces ofthe thin solid state laser medium. Especially, since a high-powerpumping source has a luminescence surface of a large size, even ifpumping light emitted out of the pumping source is focused by a lens orthe like, the pumping light has a large size in cross section at itsfocus point. Therefore, in order to pump the related art solid statelaser pumping module with a high degree of efficiency, the side surfaceswhich are-the pumping surfaces need to be enlarged. For this reason,since the thin solid state laser medium of the related art solid statelaser pumping module needs to have a large thickness and therefore thetemperature of the thin solid state laser medium which is a heatingelement increases, the efficiency of the laser oscillation and the laseroutput power decreases. On the other hand, when the thickness of thethin solid state laser medium is reduced in order to suppress thetemperature rise of the laser medium, the proportion of the pumpinglight incident upon the thin solid state laser medium is low and thisresults in decrease in the power of the output laser light.

In a related art solid state laser pumping module using a thin solidstate laser medium, which is so constructed as to introduce pumpinglight into a side surface or a plane surface of the thin solid statelaser medium, a reflecting coating which reflects light having laseroscillation wavelengths is generally formed on one plane surface of thethin solid state laser medium, and therefore the thin solid state lasermedium may be distorted under the influence of a stress produced in thereflecting coating. Since it is difficult to control the amount of thisstress distortion, the stress distortion differs every time the relatedart solid state laser pumping module is manufactured. Such thedistortion of the thin solid state laser medium causes a large loss atthe time of laser oscillation, the power of high-quality laser beams,especially the power of a single mode laser beam and low-order multimodelaser beams, is reduced greatly. Since the stress distortion differsevery time the related art solid state laser pumping module ismanufactured, the power and beam quality of the output laser lightdiffer every time the related art solid state laser pumping module ismanufactured.

Since the thin solid state laser medium has two plane surfaces which areopposite and parallel to each other, an etalon effect occurs in the thinsolid state laser medium and hence wavelength dependability of thetransmissivity of the laser light arises. For this reason, the laseroscillation does not take place throughout the gain band of the thinsolid state laser medium, and the laser oscillation is carried out atdiscontinuous wavelengths or in only a partial wavelength region. Theparallelism of the two plane surfaces of the thin solid state lasermedium which are opposite to each other may be intentionally reduced inorder to prevent such an etalon effect. However, when such a measure ofreducing the parallelism of the two plane surfaces of the thin solidstate laser medium is used, the gain distribution in a plane parallel tothe plane surfaces becomes less uniform since the thickness of the thinsolid state laser medium differs in the plane. This results indegradation in the beam quality of the output laser light and reductionin the laser power of the high-quality output laser light.

Thus, a problem with a related art solid state laser pumping moduleusing a thin solid state laser medium is that the pumping surface of thethin solid state laser medium cannot be enlarged sufficiently, and it istherefore difficult to pump the thin solid state laser medium with ahigh degree of efficiency using a high-power pumping source and hencecoexistence of improvements in the efficiency of the pumping andincrease in the power of the output laser light is difficult. Anotherproblem is that since the solid state laser medium cannot be thinnedsufficiently, the temperature rise of the solid state laser mediumbecomes large and it is therefore difficult to carry out high-efficiencyhigh-power laser oscillation. A further problem is that since the thinsolid state laser mediums distorted by a stress produced in a reflectingcoating formed on a surface of the thin solid state laser medium,high-quality output laser light cannot be obtained with a high degree ofefficiency and with high power, or the beam quality of the output laserlight degrades. A still further problem is that since it is difficult tocontrol the amount of distortion produced in the solid state lasermedium, the beam quality and power of the output laser light differevery time the related art solid state laser pumping module ismanufactured. Another problem is that since the gain distribution in aplane parallel to the surface becomes less uniform when the thickness ofthe thin solid state laser medium in the plane is varied along itslength in order to prevent an etalon effect from occurring in the thinsolid state laser medium, the beam quality of the output laser lightdegrades or the power of the high-quality output laser light decreases.

DISCLOSURE OF THE INVENTION

In accordance with the present invention, there is provided a solidstate laser pumping module including a reflecting coating formed on aplane surface of a thin solid state laser medium into which an activematerial is partially doped or doped over a whole of the plane surface,and having a structure in which heat is exhausted from the plane surfacethereof on a side of the reflecting coating. In addition, a plate-shapednon-doped medium having a refractive index close to that of the thinsolid state laser medium and having no active material is disposed onanother plane surface of the thin solid state laser medium which isopposite to the plane surface of the thin solid state laser medium onwhich the reflecting coating is formed.

Therefore, since any temperature rise of the thin solid state lasermedium can be suppressed, occurrence of stress distortions of the thinsolid state laser medium and parasitic oscillations can be prevented,and the gain region of the thin solid state laser medium can be formedinto an arbitrary shape, the present invention offers an advantage ofbeing able to provide high-power laser light with a high degree ofefficiency.

The solid state laser pumping module in accordance with the presentinvention can be so constructed as to have a pumping surface which isside surfaces of the plate-shaped thin solid state laser medium and thenon-doped medium, and via which pumping light is introduced thereinto,so that the pumping light propagates through the thin solid state lasermedium and pumps the thin solid state laser medium while being reflectedbetween the plane surface of the thin solid state laser medium on whichthe reflecting coating is formed and a plane surface of the non-dopedmedium which is opposite to the thin solid state laser medium.

Therefore, the present invention offers another advantage of being ableto enlarge the size of the pumping surface regardless of the thicknessof the thin solid state laser medium.

The solid state laser pumping module in accordance with the presentinvention can be constructed so that the pumping surface is inclinedwith respect to a direction of the thickness of the thin solid statelaser medium, and the optical axis of the pumping light outputted fromthe pumping source is inclined toward a direction which is the same as adirection toward which the pumping surface is inclined.

Therefore, the present invention offers an advantage of being able tosuppress an etalon effect and parasitic oscillations.

In the solid state laser pumping module in accordance with the presentinvention, either of diffusion bonding, optical contact, and a ceramicmanufacturing means can be used to bond the thin solid state lasermedium and the non-doped medium to each other.

Therefore, the present invention offers another advantage of being ableto provide a high-strength solid state laser chip having little opticalloss in which the thin solid state laser medium and the non-doped mediumare bonded to each other.

The solid state laser pumping module in accordance with the presentinvention can be constructed so that the plane surfaces of the thinsolid state laser medium are parallel to each other, and the planesurfaces of the non-doped medium are inclined with respect to eachother.

Therefore, the present invention offers a further advantage of beingable to suppress an etalon effect and parasitic oscillations.

In the solid state laser pumping module in accordance with the presentinvention, the active material of the thin solid state laser medium canbe Yb.

Therefore, since there is not so much influence of heat generationpeculiar to the solid state laser medium, and concentration rise andfall hardly occur, the present invention offers a still furtheradvantage of being able to reduce the physical size of the solid statelaser pumping module and to form super-short laser light pulses.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a side view of a solid state laser pumping module inaccordance with embodiment 1 of the present invention;

FIG. 2 is a diagram showing the structure of a main part of the solidstate laser pumping module in accordance with embodiment 1 of thepresent invention;

FIG. 3 is a side view of a solid state laser chip in accordance withembodiment 1 of the present invention;

FIG. 4 is a block diagram of a laser oscillator which employs the solidstate laser pumping module in accordance with embodiment 1 of thepresent invention;

FIG. 5 is a block diagram of another example of the laser oscillatorwhich employs the solid state laser pumping module in accordance withembodiment 1 of the present invention;

FIG. 6 is a diagram showing the structure of a main part of a secondexample of the solid state laser pumping module in accordance withembodiment 1 of the present invention;

FIG. 7 is a diagram showing the structure of a main part of a thirdexample of the solid state laser pumping module in accordance withembodiment 1 of the present invention;

FIG. 8 is a plan view of a fourth example of the solid state laserpumping module in accordance with embodiment 1 of the present invention;

FIG. 9 is a diagram showing the structure of a main part of a solidstate laser pumping module in accordance with embodiment 2 of thepresent invention;

FIG. 10 is a plan view of a thin solid state laser medium compositematerial of a solid state laser chip in accordance with embodiment 3 ofthe present invention; and

FIG. 11 is a side view of the solid state laser chip in accordance withembodiment 3 of the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

Hereafter, in order to explain this invention in greater detail, thepreferred embodiments of the present invention will be described withreference to the accompanying drawings.

Embodiment 1

FIG. 1 is a side plan view of a solid state laser pumping module inaccordance with embodiment 1, and FIG. 2 is a diagram showing thestructure of a main part of the solid state laser pumping module inaccordance with embodiment 1.

The solid state laser pumping module 1 in accordance with embodiment 1is provided with a solid state laser chip 2, a pumping source 20, and acooling means 8, as shown in FIGS. 1 and 2. The solid state laser chip 2is comprised of a thin solid state laser medium 3, a non-doped medium 4,and a reflecting coating 6.

The thin solid state laser medium 3 is a laser medium into which a rareearth material is doped as an active material, and includes, as its basematerial, such a material as a crystal, ceramics, or glass material. Inthis embodiment, although the rare earth material doped into the thinsolid state laser medium is not limited and any of various rare earthmaterials can be used as the doped rare earth material, a case where Yb(ytterbium) is used as the doped rare earth material will be explainedhereafter. Furthermore, although the base material of the thin solidstate laser medium is not limited in this embodiment and any of variousbase materials can be used as the base material of the thin solid statelaser medium, a case where Y₃Al₅O₁₂ (YAG) is used as the base materialof the thin solid state laser medium will be explained hereafter. SuchYAG into which Yb is doped is called Yb:YAG.

The non-doped medium 4 is formed on a surface of the thin solid statelaser medium 3 which is opposite to another surface of the thin solidstate laser medium 3 on which the reflecting coating 6 is formed, and isplate-shaped and is optically transparent. The non-doped medium 4 has arefractive index close to that of the thin solid state laser medium 3,but does not have the active material which is doped into the thin solidstate laser medium 3. In other words, either of a crystal, ceramics, orglass material, or the like can be used as the non-doped medium 4, as inthe case of the base material of the thin solid state laser medium 3,and no laser material is doped into the non-doped medium 4.

The solid state laser chip 2 in accordance with this embodiment ispumped by the pumping source 20 from a lateral side surface thereof. Inthe solid state laser chip 2, since the thin solid state laser medium 3and the non-doped medium 4 are bonded to each other so that they areintegral with each other, a light incidence surface via which pumpinglight from the pumping source is incident into the solid state laserchip is the lateral side surface which is a united one of a lateral sidesurface of the thin solid state laser medium 3 and a lateral sidesurface of the non-doped medium 4. This united surface is a pumpingsurface 9. The pumping light source 20 can be a semiconductor laser.Especially, the pumping light source 20 can be a semiconductor laser barwhich can efficiently emit high-power pumping light. For example, thepumping light source 20 has a semiconductor laser 21 including asingle-layer semiconductor laser bar 22 so as to pump the solid statelaser chip. The semiconductor laser bar 22 can have a light emittingsurface having a size of several micrometers in a direction of the fastaxis thereof, and having a size of about 10 mm in a direction of theslow axis thereof. In such a case, when the solid state laser pumpingmodule is formed so that the pumping surface 9 has a size in a direction(referred to as a width direction) perpendicular to the direction of thethickness of the solid state laser chip 2, the size being equal to orlarger than that of the semiconductor laser 21 in the direction of theslow axis thereof, and the distance between the semiconductor laser bar22 and the pumping surface 9 is equal to or shorter than the distance ofthe solid state laser chip 2 in the direction of the thickness thereof,almost all the pumping light can be efficiently incident upon the solidstate laser chip 2 via the pumping surface 9. The pumping light 23incident upon the solid state laser chip 2 via the pumping surface 9propagates through the solid state laser chip 2 while being repeatedlytotal-reflected within the solid state laser chip 2. When thepropagating pumping light 23 passes through the thin solid state lasermedium 3, the pumping light 23 is absorbed by the thin solid state lasermedium 3. Thus, while the pumping light 23 propagates zigzag through theinterior of the solid state laser chip 2, it is absorbed by the thinsolid state laser medium 3 and the thin solid state laser medium 3 ispumped by the pumping light.

The semiconductor laser light is emitted in the direction of the firstaxis of the semiconductor laser with a large spread angle. For example,the semiconductor laser light can be emitted out of the semiconductorlaser with a spread angle of 40 degrees at full width at half maximum.Therefore, since light components having large spread angles of thepumping light 23 which is incident upon the solid state laser chip viathe pumping surface 9 are incident upon the surface of the thin solidstate laser medium 3 (referred to as a lower surface of the solid statelaser chip from here on), on which the reflecting coating 6 is formed,at large angles, and are also incident upon a surface of the non-dopedmedium 4 (referred to as an upper surface of the solid state laser chipfrom here on), which is opposite to another surface of the non-dopedmedium 4 which is bonded to the thin solid state laser medium, at largeangles, those light components are total-reflected by the lower andupper surfaces. Therefore, when propagating through the interior of thesolid state laser chip, the light components having large spread anglesof the pumping light 23 are total-reflected a large number of times bythe upper and lower surfaces of the solid state laser chip andpropagates zigzag. On the other hand, other light components havingsmall spread angles of the pumping light 23 propagates through theinterior of the solid state laser chip while being total-reflected asmall number of times by the upper and lower surfaces of the solid statelaser chip.

Assuming that the thin solid state laser medium which constitutes thesolid state laser chip in accordance with the present invention has athickness of d1 and the non-doped medium has a thickness of d2, thesolid state laser chip has a thickness of d0 equal to d1+d2.Furthermore, it is assumed that a related art thin solid state lasermedium has a thickness of D1, and has a size of L in a direction of itslength which is perpendicular to the pumping surface thereof. Forexample, when the thickness d1 of the thin solid state laser medium ofthe solid state laser chip in accordance with the present invention isequal to the thickness D1 of the related art thin solid state lasermedium and the thickness d1 of the thin solid state laser medium is mtimes the thickness d2 of the non-doped medium, d1=D1, d2=m×d1, andd0=d1+d2=(m+1)d1.

It can be therefore seen that in accordance with this embodiment, sincethe pumping surface of the thin solid state laser medium in accordancewith the present invention has a size which is (m+1) times that of thepumping surface of the related art thin solid state laser medium and theaperture of the pumping surface of the thin solid state laser medium inaccordance with the present invention is (m+1) times that of the pumpingsurface of the related art thin solid state laser medium, the pumpinglight can be easily made to be incident upon the solid state laser chipin accordance with the present invention via the pumping surface. On theother hand, since the pumping light is not absorbed by the solid statelaser chip 2 in accordance with this embodiment when passing through thenon-doped medium 4, an absorption length which is equal to a lengthwhich the pumping light passes through the solid state laser medium isreduced to 1/(m+1) of that of the related art thin solid state lasermedium.

Therefore, in order to provide an absorption length equal to that of therelated art thin solid state laser medium, the thin solid state lasermedium in accordance with the present invention needs to have a sizewhich is (m+1) times that of the related art thin solid state lasermedium, i.e., a size of (m+1)L in the direction of its length which isperpendicular to the pumping surface thereof. In this case, the thinsolid state laser medium in accordance with the present invention canprovide an absorption equal to that provided by the related art thinsolid state laser medium. In addition, since the absorption rate perunit length of the pumping light increases with increase in theconcentration of the active material contained in the thin solid statelaser medium, the absorption rate can be kept constant even when theabsorption length is short.

For example, since the absorption rate per unit length also becomes(m+1) times that of the related art thin solid state laser medium whenthe concentration of the active material is increased to (m+1) timesthat of the active material contained in the related art thin solidstate laser medium, the same absorption rate as that of the related artthin solid state laser medium can be secured even when the absorptionlength is reduced to 1/(m+1) of that of the related art thin solid statelaser medium. Especially, when the active material is Yb and the basematerial is YAG, it is possible theoretically to replace 100% of YAGwith Yb. It is therefore easy to dope a high concentration of Yb intoYAG so as to provide a large absorption rate per unit length.

Therefore, since the solid state laser pumping module in accordance withthis embodiment employs the solid state laser chip 2 in which the thinsolid state laser medium 3, into which a high concentration of activematerial is doped, and the non-doped medium 4 are bonded to each other,it is possible to widen the pumping surface without thickening the thinsolid state laser medium 3 and it is possible to make the pumping lightbe absorbed by the thin solid state laser medium 3 without enlarging theouter size of the solid state laser chip 2.

Thus, since the size of the pumping surface in the direction of thethickness of the solid state laser chip can be enlarged, a pumpingsource having a large light emitting surface, such as a laminatedsemiconductor laser bar, can be alternatively used. In this case, thesolid state laser pumping module can be pumped with high power andtherefore high-power output laser light can be obtained.

The temperature of the thin solid state laser medium which is a heatingelement increases with increase in its thickness. In the solid statelaser pumping module in accordance with this embodiment, since thethickness of the thin solid state laser medium 3 can be thinnedregardless of the pumping source, it is possible to sufficiently reducethe thickness of the thin solid state laser medium 3. As a result, theincrease in the temperature of the thin solid state laser medium 3 canbe suppressed to a very small value. Thus, since the increase in thetemperature of the thin solid state laser medium 3 is small, laseroscillation can be carried out with a high degree of efficiency and withhigh power. Furthermore, when a laser amplifier is so constructed as tohave this structure, the laser amplifier can have a high gain. In thiscase, the laser amplifier can provide energy with a high degree ofefficiency and carry out high-power amplification.

In a case where heat is exhausted from an end surface of the thin solidstate laser medium, a reflecting coating for reflecting light having awavelength equal to that of laser light incident upon the solid statelaser module is formed on the end surface of the thin solid state lasermedium from which heat is exhausted and the thin solid state lasermedium is used as a reflecting mirror having a gain. The thinner thethickness of the thin solid state laser medium, the smaller the increasein the temperature of the thin solid state laser medium, and the thinnerthickness of the thin solid state laser medium is advantageous forgreater efficiency of the laser oscillation and greater power, aspreviously mentioned. On the other hand, when the thickness of the thinsolid state laser medium is too thin, distortion may occur in the thinsolid state laser medium due to a stress by the reflecting coating.Although the distorted thin solid state laser medium operates as areflecting surface having a curvature, the distortion does not have anideal spherical or parabolic distribution, but the distorted thin solidstate laser medium becomes a reflecting surface with a high orderaberration. Since the high order aberration cannot be corrected easilyby neither a spherical lens nor a cylindrical lens, the laser beamquality degrades and the laser power decreases depending on the amountof the produced aberration. In general, since it is difficult to controlthe stress by the reflecting coating, it is difficult to control theamount of the distortion. For this reason, a related art solid statelaser chip differs in its laser beam quality and output every time it ismanufactured.

In contrast, the solid state laser chip 2 in accordance with thisembodiment is constructed so that the surface of the thin solid statelaser medium 3 which is opposite to the other surface on which thereflecting coating 6 is formed is optically bonded to the non-dopedmedium 4. The non-doped medium 4 has a larger thickness than the thinsolid state laser medium 3, and is bonded to the thin solid state lasermedium 3 over the whole surface thereof. Thus, since the thin solidstate laser medium 3 and the non-doped medium 4 are bonded to each otherover the whole surfaces thereof, the solid state laser chip 2 hasgreater rigidity than the single thin solid state laser medium 3 and theamount of distortion that occurs in the solid state laser chip 2 due toa stress by the reflecting coating 6 becomes very small. For thisreason, the solid state laser pumping module in accordance with thepresent invention exhibits a characteristic in which neither degradationof the beam quality of the output laser light depending on distortionthat occurs in the solid state laser chip nor decrease in the power ofthe laser light with a high beam quality occurs, and the solid statelaser pumping module can provide a high-beam-quality high-power laseroutput. Furthermore, while the solid state laser pumping module inaccordance with the present invention does not exhibit a characteristicin which the output laser light differs in its power and beam qualityevery time it is manufactured, the solid state laser pumping module hasan advantage of being able to provide a stable-quality laser outputhaving stable power.

In accordance with this embodiment, the thin solid state laser medium 3and the non-doped medium 4 can be bonded to each other using a techniquecalled diffusion bonding. According to the diffusion bonding, the thinsolid state laser medium 3 and the non-doped medium 4 are boned to eachother by heating their surfaces to be bonded to each other to hightemperatures after exerting a pressure on the two surfaces. Thus, thebonded surfaces have little optical loss and have a large strength.According to the diffusion bonding, when two materials to be bonded toeach other have refractive indices close to each other, they can bebonded to each other with a high degree of quality. Therefore, the basematerial of the thin solid state laser medium 3 can be the same as thematerial from which the non-doped medium 4 is made. For example, whenthe thin solid state laser medium 3 is Yb:YAG, the non-doped medium 4can be YAG. In this case, Yb:YAG and YAG can be handled as a chip havinggreat rigidity and having no optical loss.

The solid state laser chip 2 in which the thin solid state laser medium3 and the non-doped medium 4 are bonded to each other as one chip ispumped by the pumping source 20. Since no active material is doped intothe non-doped medium 4, but an active material is doped into only thethin solid state laser medium 3, the pumping light 23 is absorbed onlyby the thin solid state laser medium 3. Therefore, heat is generatedonly in the thin solid state laser medium 3, whereas no heat isgenerated in the non-doped medium 4.

Heat is exhausted from the surface of the thin solid state laser medium3 on which the reflecting coating 6 is formed. For this reason, theincrease in the temperature of the thin solid state laser medium 3 ofthe solid state laser chip 2 is the same as that in the temperature of asingle thin solid state laser medium having the same thickness as thethin solid state laser medium 3 of the solid state laser chip 2 andhaving the same amount of heat generation as the thin solid state lasermedium 3. Therefore, even when the thickness of the thin solid statelaser medium 3 in a direction of heat transfer is thinned to 100micrometers or less, the solid state laser chip has great rigidity andthe distortion due to the stress by the reflecting coating 6 is verysmall, and the increase in the temperature of the thin solid state lasermedium can be suppressed to a low value because the thin solid statelaser medium is bonded to the non-doped medium 4. Thus, in accordancewith this embodiment, since the distortion of the solid state laser chip2 can be reduced greatly, neither degradation of the laser beam qualitynor decrease in the laser power occurs. Furthermore, since the thicknessof the thin solid state laser medium 3 can be thinned, the solid statelaser pumping module offers an advantage of being able to reduce theincrease in the temperature of the thin solid state laser medium and toprovide high-power laser light with a high degree of efficiency.

As described above, the solid state laser chip 2 is the one in which thethin solid state laser medium 3 and the non-doped medium 4 are bonded toeach other using diffusion bonding. As an alternative, the solid statelaser chip 2 in which the thin solid state laser medium 3 and thenon-doped medium 4 are bonded to each other can be formed using anoptical contact technique or a ceramic manufacturing technique forunifying two powdered media by laminating and sintering them. Aspreviously mentioned, the base material of the thin solid state lasermedium is the same as the material from which the non-doped medium ismade. As an alternative, the non-doped medium 4 can be made from amaterial that is optically transparent, and that has a refractive indexclose to that of the thin solid state laser medium 3. In this variant,the above-mentioned diffusion bonding or the technique for manufacturingceramics can be similarly used to bond the thin solid state laser medium3 and the non-doped medium 4 together. For example, the thin solid statelaser medium 3 can be Yb:YAG, and the non-doped medium can be made fromsapphire. Since the sapphire is an optically-transparent high-rigiditymaterial, and has a feature of being able to reduce the amount ofdistortion in the non-doped medium due to stress to a very small one.

The cooling means 8 is bonded to the surface of the thin solid statelaser medium 3, on which the reflecting coating 6 is formed, with abonding agent 7. The bonding agent 7 can be an adhesive, metallicmaterial, or alloy. For example, a metallic film, such as a gold orcopper film, is formed on the reflecting coating 6 and the metallic filmis alloyed with a solder material such as indium, so that the coolingmeans 8 is bonded to the reflecting coating formed on the thin solidstate laser medium 3. When the cooling means 8 is thus bonded to thereflecting coating formed on the thin solid state laser medium 3, thebonding strength is enhanced and the thermal resistance is reduced.

A heat sink which constitutes the cooling means 8 can have a suitablechannel through which such a cooling medium as a fluid or gas is passed.In this case, water, ethylene glycol, alcohol, ammonia, mercury, liquidnitrogen, liquid helium, or the like can be used as the fluid, and ahelium gas or the like is suitable for the gas. As an alternative, thecooling means 8 can be bonded to a plate which is independently cooled,or can be bonded to a Peltier element so that it is cooled by thePeltier element. In either of the cases, since the solid state laserchip 2 is constructed so that the surface of the thin solid state lasermedium 3 on which the reflecting coating 6 is formed is thermally andmechanically bonded to the heat sink 8 with the bonding agent 7, theheat produced in the thin solid state laser medium 3 flows in a singledimension toward the cooling means 8. For this reason, in the thin solidstate laser medium 3, a temperature distribution occurs only in a crosssection in the direction of the thickness thereof, and the thin solidstate laser medium 3 has a temperature distribution in which thetemperature of the surface thereof on which the reflecting coating 6 isformed is the lowest and that of the other surface thereof to which thenon-doped medium 4 is bonded is the highest. On the other hand, sinceheat conduction is carried out in a single dimension within the solidstate laser chip 2, no temperature distribution occurs in a planeperpendicular to the direction of the thickness of the solid state laserchip 2, i.e., a plane parallel to the cross section of the laser beamwhich is pumped by the solid state laser chip, and therefore no heatlens effect is produced. Therefore, the present embodiment offers anadvantage of being able to prevent the operational stability region fromchanging in connection with the pumping or the laser power, and beingable to provide a high-power high-quality laser beam with stability.

The thin solid state laser medium, which is pumped by the pumping lightof sufficient intensity, produces fluorescence and has an optical gain.For this reason, laser oscillation can be carried out when a suitablepartial reflection mirror is arranged so that a resonator isconstructed. On the other hand, since the thin solid state laser mediumis thin and has an optical gain in its small region, there is apossibility that a not-intended laser oscillation takes place. Forexample, laser oscillation may take place between the two upper andlower surfaces of the thin solid state laser medium or between sidesurfaces of the thin solid state laser medium which are opposite to eachother, or produced fluorescence may be total-reflected repeatedlybetween the above-mentioned two surfaces of the thin solid state lasermedium and increase the amount of fluorescence, so that the optical gainof the solid state laser chip is reduced. This phenomenon is calledoccurrence of ASE (Amplified Spontaneous Emission). In extreme cases, anunnecessary laser oscillation which is called a parasitic oscillationtakes place. Since the parasitic oscillation cannot be taken out of thesolid state laser chip as a desired laser beam, and reduces the opticalgain of the solid state laser chip, the power of the desired laser beamemitted out of the output mirror may be saturated and may be furtherreduced even if the power of the pumping light applied to the solidstate laser chip is increased. For this reason, in the case of a thinmedium made from Yb:YAG in which a small region has to be pumped byhigh-power-density pumping light, there is particularly a necessity tosuppress parasitic oscillations as mentioned above.

When a thin solid state laser medium is used alone without being bondedto a non-doped medium, fluorescence which is produced at an angle whichsatisfies total reflection conditions within the thin solid state lasermedium is repeatedly total-reflected between the two upper and lowersurfaces of the thin solid state laser medium, and therefore reduces theoptical gain of the thin solid state laser medium. On the other hand, inthe case of the solid state laser chip 2 in accordance with the presentinvention, since fluorescence produced in the thin solid state lasermedium 3 is total-reflected between the upper and lower surfaces of thesolid state laser chip 2, the length through which the producedfluorescence is passed within the thin solid state laser medium becomesshort by a length corresponding to the thickness of the non-doped mediumbonded to the thin solid state laser medium, and the amount of reductionin the optical gain of the thin solid state laser medium is reduced.Therefore, the solid state laser pumping module in accordance with thepresent invention offers an advantage of being able to prevent parasiticoscillations from easily occurring and to provide a high-power laserbeam with a high degree of efficiency.

The solid state laser chip 2 can be constructed so that the parallelismof the two upper and lower surfaces thereof is reduced in order tosuppress parasitic oscillations.

When a parallel plate exists in a laser cavity, wavelength dependabilitywhich is called an etalon effect and by which only a light beam having aresonance wavelength is selectively amplified may occur under theinfluence of optical resonance caused by reflection at both end surfacesof the parallel plate. In the case of a related art solid state laserpumping module in which a reflecting coating is formed on a lowersurface of a thin solid state laser medium and has a high reflectivity,an etalon effect may occur in the thin solid state laser medium underthe influence of multipath reflection between the upper and lowersurfaces of the thin solid state laser medium even if the reflectivityof the upper surface is small. In the case of a single thin solid statelaser medium, there is a necessity to reduce the parallelism of theupper and lower surfaces of the thin solid state laser medium itself inorder to reduce the etalon effect between the upper and lower surfacesof the thin solid state laser medium. Thus, when the single thin solidstate laser medium is so constructed, the thickness of the laser mediumhaving a gain differs from position to position in the cross section ofthe laser beam. Therefore, since the amplification factor of the lasermedium differs from position to position in the cross section of thelaser beam, the beam quality of the laser beam may degrade.

In order to solve this problem, in accordance with this embodiment, theparallelism of the two upper and lower surfaces of the plane-shapedsolid state laser chip 2 is intentionally reduced, as shown in FIG. 3.As shown in this figure, the free surface of the non-doped medium, whichis opposite to the other surface of the non-doped medium to which thethin solid state laser medium 3 is bonded, is inclined with respect tothe other surface, and is called an inclined surface 92 of the non-dopedmedium. Thus, since the non-doped medium 4 has the inclined surface 92,the optical paths of light beams repeatedly reflected between the upperand lower surfaces of the solid state laser chip 2 are not in agreementwith one another, and multiplex interference does not take place. Forthis reason, since no etalon effect occurs and the light beam passingthrough the solid state laser chip does not have wavelengthdependability, continuous laser oscillation and amplification can becarried out in a laser gain band and ideal formation of super-shortlaser pulses can be carried out.

Since the solid state laser chip 2 of this variant is constructed sothat the thin solid state laser medium 3 and the non-doped medium 4having the inclined plane 92 are bonded to each other, the etalon effectand parasitic oscillations can be suppressed even though the thicknessof the thin solid state laser medium having a gain is kept constant overthe length thereof. Therefore, the present embodiment offers anadvantage of being able to provide a high-quality laser beam withoutdegrading the beam quality of the laser beam since the amplificationfactor of the solid state laser medium is kept constant over the crosssection of the laser beam. This variant of the present embodiment offersanother advantage of suppressing parasitic oscillations resulting fromreflection at the upper and lower surfaces of the solid state laser chip2. As shown in FIG. 3, in accordance with this variant, by changing thethickness of the non-doped medium 4 along the direction perpendicular tothe two pumping surfaces 9, the parallelism of the upper and lower sidesurfaces of the solid state laser chip is reduced. As an alternative,the parallelism of the upper and lower side surfaces of the solid statelaser chip can be reduced by changing the thickness of the non-dopedmedium 4 along a direction perpendicular to side surfaces of the solidstate laser chip other than the two pumping surfaces.

Next, a laser oscillator using the solid state laser pumping module 1which is constructed as mentioned above will be explained.

FIGS. 4 and 5 are block diagrams showing the laser oscillator whichemploys the solid state laser pumping module 1 in accordance with thisembodiment. FIG. 4 shows an example of a laser cavity in which an outputmirror 31 is arranged opposite to the solid state laser chip 2, and FIG.5 shows another example of the laser cavity when the solid state laserchip has a size in a direction of an Y axis which is larger than that ina direction of an X axis. Only minimum optical components required forperforming the laser oscillation are shown in these figures, and variousoptical components can be further added to either of those cases.

In the case of the structure shown in FIG. 4, the output mirror 31 isarranged so that its optical axis is aligned with laser resonance light32, and the solid state laser chip 2 is also arranged so that itsoptical axis is aligned with output light 33. The laser resonance light32 goes back and forth between the solid state laser chip 2 and theoutput mirror 31, and the output laser light 33 is outputted from theoutput mirror 31. When the semiconductor laser has a length in adirection of its slow axis of (i.e., in the direction of the Y axis inthe figure) which is equal to the length in a direction in which thepumping light propagates (i.e., in the direction of the X axis in thefigure) and the solid state laser chip has an XY cross section close toa square in shape, the construction of the laser cavity easily makes thequality in the direction of the X axis of the laser beam obtained by thelaser oscillation be equal to that in the direction of the Y axis. Whenother optical components are arranged so that a single mode resonator isconstructed, a laser beam having equal beam diameters in the directionsof the X and Y axes can be provided.

In the case of the structure shown in FIG. 5, the solid state laser chip2 is used as one reflecting mirror having an optical gain. Whileresonance light 32 is almost perpendicular to the X-axis, it is inclinedwith respect to the Y-axis and is reflected by the solid state laserchip 2. For this reason, the optical axis of resonance light incidentupon the solid state laser chip 2 is not aligned with that of resonancelight which is emitted out of the solid state laser chip 2. Therefore, areflecting mirror 30 is further arranged so as to be aligned with theoptical axis of the resonance light which is incident upon or is emittedout of the solid state laser chip 2, and an output mirror 31 is arrangedso as to be aligned with the optical axis of the other resonance lightemitted out of the solid state laser chip. Thus, since the reflectingmirror 30 and the output mirror 31 are optically arranged so that theysandwich the solid state laser chip 2, the laser resonance light 32passes through the solid state laser chip 2 having an optical gain twotimes while the laser resonance light 32 makes a round trip between thereflecting mirror 30 and the output mirror 31. For this reason, theoptical gain of the solid state laser chip 2 can be assumed to have anincreased optical gain as compared with the case where the solid statelaser chip 2 is used as a reflecting mirror placed at an end of thelaser cavity.

In addition, the laser resonance light 32 is perpendicular to the X-axisof the solid state laser chip 2, and is not perpendicular to the Y-axisof the solid state laser chip 2 and has a certain angle with respect tothe Y-axis. Therefore, the solid state laser chip 2 can seemingly have asquare shape other than a rectangular shape with respect to the laserresonance light 32. Therefore, this laser oscillator offers an advantageof being able to provide laser output light having an equal beamdiameter in all directions in the cross section even though the size inthe direction of the Y axis of the solid state laser chip 2 is largerthan that in the direction of the X axis, and to provide laser outputlight having an equal beam diameter in all directions in the crosssection even when a single mode resonator is constructed. In a casewhere the solid state laser chip 2 has a size in the direction of the Xaxis which is larger than that in the direction of the Y axis, the sameadvantage is provided even if the reflecting mirror 30 and the outputmirror 31 are arranged so that the laser resonance light 32 is inclinedwith respect to the X-axis.

Next, a case where a laminated semiconductor laser bar in which two ormore semiconductor laser bars are laminated in the direction of the fastaxis of the semiconductor laser is used as the pumping source will beexplained as a second example.

FIG. 6 is a block diagram showing a main part of the solid state laserpumping module of the second example. As semiconductor lasers which canproduce high-power pumping light, there has been provided asemiconductor laser bar having a bar-shaped luminescence surface.

However, since the optical power which can be outputted from onesemiconductor laser bar is restricted, there has been provided asemiconductor laser having a structure in which two or more bars arelaminated in the direction of the fast axis of the semiconductor laserin order to increase its optical output. FIG. 6 shows the semiconductorlaser in which four semiconductor laser bars are laminated in thedirection of the fast axis of the semiconductor laser. For this reason,the optical output of the semiconductor laser becomes four times ascompared with a case where only a single semiconductor laser bar isused, and high-power pumping can be achieved. Although the figure showsthe case where four semiconductor laser bars are laminated, the numberof semiconductor laser bars laminated in the semiconductor laser is notlimited to four. The semiconductor laser can include n bars (n is aninteger) laminated therein. Thus, since the first semiconductor laserbar 22.1, the second semiconductor laser bar 22.2, the thirdsemiconductor laser bar 22.3, and the 4th semiconductor laser bar 22.4are laminated in the direction of the fast axis of the semiconductorlaser 21 or the first semiconductor laser bar 22.1 to the n-thsemiconductor laser bar 22.n (n is an integer) are laminated in thedirection of the fast axis of the semiconductor laser 21, the pumpinglight has total output power which is four times (or n times) that ofpumping light generated by a single semiconductor laser bar. This typeof semiconductor laser is called a laminated semiconductor laser bar.

When using such a laminated semiconductor laser bar in which a pluralityof semiconductor laser bars are laminated in the direction of the fastaxis of the laminated semiconductor laser bar, each pumping light beamemitted out of the semiconductor laser has a large area in the directionof the fast axis of the semiconductor laser bar. It is difficult forrelated art solid state pumping modules to use an optical output from alarge luminescence surface with a high degree of efficiency. Incontrast, in accordance with this embodiment, since the thin solid statelaser medium 3 and the non-doped medium 4 are bonded to each other, thesize of each pumping surface 9 in the direction of the fast axis can beenlarged by enlarging the thickness of the non-doped medium 4 while thethickness of the thin solid state laser medium 3 is kept constant. Thefirst pumping light 23.1, the second pumping light 23.2, the thirdpumping light 23.3 and the fourth pumping light 23.4, or the firstpumping light 23.1 to the n-th pumping light 23.n (n is an integer),which are incident upon the solid state laser chip via each pumpingsurface 9, propagate through the interior of the solid state laser chip2 while being total-reflected by the upper and lower surfaces of thesolid state laser chip 2, and are absorbed by the thin solid state lasermedium 3 while passing through the thin solid state laser medium 3.Thus, only the arrangement of the high-power laminated semiconductorlaser bar in the vicinity of the solid state laser chip 2 makes itpossible to pump the thin solid state laser chip 3 with a high degree ofefficiency. As a result, this second example offers an advantage ofbeing able to provide high-power laser output light 33 with a highdegree of efficiency.

Next, a case where a laminated semiconductor laser bar in which two ormore bars are laminated in the direction of the fast axis of thelaminated semiconductor laser bar is used as the pumping source and acylindrical lens array and a focusing optical system are further usedwill be explained as a third example.

FIG. 7 is a block diagram showing a main part of the solid state laserpumping module of the third example. Pumping light outputted from eachsemiconductor laser bar has a large spread angle in the direction of thefast axis thereof. Therefore, in accordance with this example, a microcylindrical lens is arranged for each semiconductor laser bar in orderto collimate the pumping light emitted out of each semiconductor laserbar having a large spread angle in the direction of the fast axisthereof. Each micro cylindrical lens has a curvature in the direction ofthe fast axis of a corresponding semiconductor laser bar, and nocurvature in the direction of the slow axis of the correspondingsemiconductor laser bar. Each micro cylindrical lens, which is arrangedin the vicinity of the corresponding semiconductor laser bar so that theoptical axis of each micro cylindrical lens is aligned with the pumpinglight outputted from the corresponding semiconductor laser bar, cancollimate the pumping light having a large spread angle in the directionof the fast axis, which is emitted out of the correspondingsemiconductor laser bar, while each micro cylindrical lens does not haveany influence upon a spread angle of the pumping light in the directionof the slow axis of the corresponding semiconductor laser bar. While thelaminated semiconductor laser bar has the two or more semiconductorlaser bars, two or more micro cylindrical lenses are also arranged sothat they correspond to the plurality of semiconductor laser bars,respectively. The plurality of micro cylindrical lenses laminated arecalled a cylindrical lens array. For example, as shown in FIG. 7, thefirst pumping light emitted out of the first semiconductor laser bar22-1 is collimated by the first micro cylindrical lens 40-1, the secondpumping light emitted out of the second semiconductor laser bar 22-2 iscollimated by the second micro cylindrical lens 40-2, the third pumpinglight emitted out of the third semiconductor laser bar 22-3 iscollimated by the third micro cylindrical lens 40-3, and the fourthpumping light emitted out of the fourth semiconductor laser bar 22-4 iscollimated-by the fourth micro cylindrical lens 40-4, or the firstthrough n-th pumping light beams respectively emitted out of the firstthrough n-th, not shown, semiconductor laser bars are collimated by thefirst through n-th micro cylindrical lenses (n is an integer). Thus,since the plurality of pumping light beams respectively emitted out ofthe plurality of laminated semiconductor laser bars which are thusarranged are individually collimated by the cylindrical lenses of thecylindrical lens array, the plurality of light beams which are allcollimated when viewed from the direction of the fast axis areoutputted.

The plurality of pumping light beams which are individually collimatedby the plurality of cylindrical lenses of the cylindrical lens array arecollectively focused by the focusing optical system 41. The focusingoptical system can focus the pumping light from each semiconductor laserbar in both the directions of the fast axis and slow axis of the pumpinglight source, or can focus the pumping light from each semiconductorlaser bar only in the direction of the fast axis of the pumping lightsource. A plurality of cylindrical lenses can be combined and arrangedas the focusing optical system, or a plurality of circular lenses areconcentrically arranged in a line as the focusing optical system.Furthermore, each of those lenses can have a spherical surface or anaspheric surface. In either case, in order to make each pumping lightbeam emitted out of the pumping source be incident upon the solid statelaser chip 2 via the pumping surface 9, the focusing optical systemreduces the cross-sectional size of each pumping light. In accordancewith the present embodiment, the focusing optical system is comprised oftwo cylindrical lenses, for example. The first cylindrical lens 42 has acurvature in the direction of the slow axis of the pumping light source,and is arranged so that the optical axis thereof is aligned with all thepumping light beams collimated by the cylindrical lens array, and thesecond cylindrical lens 43 is arranged between the first cylindricallens and the solid state laser chip 2 so that the optical axis thereofis aligned with all the pumping light beams collimated by thecylindrical lens array.

Each pumping light emitted out of the laminated semiconductor laser bar22 is outputted with a slight spread angle in the direction of the slowaxis of the pumping light source. Since the cylindrical lens array doesnot have any curvature in the direction of the slow axis of the pumpinglight source, each pumping light emitted out of the laminatedsemiconductor laser bar has no change in its optical path in thedirection of the slow-axis when passing through the cylindrical lensarray. Each pumping light which has passed through the cylindrical lensarray and is incident upon the first cylindrical lens having a curvaturein the direction of the slow axis of the pumping light source propagateswhile being focused by a lens action of the first cylindrical lens afterpassing through the first cylindrical lens Although the secondcylindrical lens 43 is arranged in front of a focal point of the firstcylindrical lens 42, each pumping light has no change in the opticalaxis thereof in the direction of the slow axis, and passes through thesecond cylindrical lens 43 while being focused because the secondcylindrical lens 43 has no curvature in the direction of the slow axis.Thus, since each pumping light is focused in the direction of the slowaxis of the pumping light source by the first cylindrical lens 42 afteremitted out of the laminated semiconductor laser bar 22 (i.e., acorresponding one of the plurality of semiconductor laser bars 22-1 to22-4), the beam diameter of each pumping light in the direction of theslow axis becomes small. For this reason, the solid state laser chip 2can be reduced in size to smaller than the laminated semiconductor laserbar 22. All the pumping light beams can be made to be incident upon thesolid state laser chip 2 via the pumping surface 9 by slightly enlargingthe size of the solid state laser chip 2 in the direction of the slowaxis of the pumping light source as compared with the beam size of allthe pumping light beams at the focusing position. Thus, since the sizeof the solid state laser chip 2 in the direction of the slow axis can bereduced, the thin solid state laser medium 3 can be pumped by thehigh-power-density pumping light. Since the thin solid state lasermedium can be pumped by the high-power-density pumping light, thelow-level absorption is saturated and the amount of pumping powerrequired for obtaining a desired optical gain is reduced. As a result,the laser oscillation threshold can be reduced and therefore the solidstate laser pumping module can output a high-power laser beam with ahigh degree of efficiency.

The pumping light is emitted out of the laminated type semiconductorlaser bar 22 with a large spread angle in the direction of the fast axisof the laminated semiconductor laser bar 22. Since the cylindrical lensarray has a curvature in the direction of the fast axis of the laminatedtype semiconductor laser bar, the pumping light is collimated whenpassing through the cylindrical lens array. All the pumping light beamswhich are respectively emitted out of the plurality of semiconductorlaser bars and are collimated by the cylindrical lens array are thenincident upon the first cylindrical lens 42. Since the first cylindricallens 42 does not have any curvature in the direction of the fast axis ofthe laminated semiconductor laser bar, all the pumping light beams passthrough the first cylindrical lens 42 with their parallelism beingmaintained. All the pumping light beams are further incident upon thesecond cylindrical lens 43 which is so arranged as to be aligned withthe first cylindrical lens. Since this second cylindrical lens has acurvature in the direction of the fast axis of the laminatedsemiconductor laser bar, each collimated light beam is focused to afocal position. The focal distance of the second cylindrical lens is setso as to be shorter than that of the first cylindrical lens, so that thefocal position of the focusing optical system in the direction of theslow axis of the laminated semiconductor laser bar can be made to be inagreement with the focal position of the focusing optical system in thedirection of the fast axis of the laminated semiconductor laser bar. Asa result, all the pumping light beams can have a minimized beam diameterat the focal position of the focusing optical system. Therefore, sincethe area of the pumping surface 9 can be reduced by arranging thepumping surface 9 of the solid state laser chip 2 at this focalposition, the solid state laser chip 2 can be pumped with high-densitylight power. As a result, this example offers an advantage of being ableto provide a high-power laser beam with a high degree of efficiency.

Next, a case where two or more pumping sources are arranged around thesolid state laser chip will be explained as a fourth example.

FIG. 8 is a plan view of the solid state laser pumping module of thisexample. When there are one or more pumping surfaces on lateral sides ofthe solid state laser chip, the same advantages as provided by theabove-mentioned embodiment are offered. On the other hand, when two ormore pumping sources are arranged around the solid state laser chip 2,the power of the pumping light can be increased and therefore ahigh-power laser output can be obtained. FIG. 8 shows the example inwhich four pumping sources are respectively arranged at four positionswhich are rotation symmetric around the solid state laser chip. Thesolid state laser chip 2 is shaped like a polygon having four or morelateral side surfaces, and four of these side surfaces are used aspumping surfaces. Since the solid state laser chip and the four pumpingsources are thus arranged, the pumping power can be increased while thesize of the solid state laser chip 2 is kept constant. Therefore, thisexample offers an advantage of being able to pump the solid state laserchip with the high-density laser power, and to provide high-power outputlaser light with a high degree of efficiency. Since the solid statelaser chip 2 is pumped from almost the entire perimeter thereof, it hasa pumped region having good rotation symmetry and a gain region havinggood homogeneity. Therefore, this example offers another advantage ofbeing able to provide a high-quality high-power laser beam with a highdegree of efficiency.

The solid state laser chip 2 in accordance with this embodiment has ashape like a square or rectangle, as mentioned above. As an alternative,the solid state laser chip 2 can have an arbitrary shape. For example,when the pumping source is a semiconductor laser or laminated typesemiconductor laser bar, it is desirable that at least the pumpingsurface at least has a plane shape. On the other hand, when the pumpinglight is emitted out of an optical fiber and fiber bundle, the pumpinglight has a small cross-sectional size not only in the direction of thethickness of the solid state laser chip but in the direction of thewidth of the solid state laser chip. Therefore, in this case, thepumping surface does not need to have a plane shape. For example, theupper and lower plane surfaces of the solid state laser chip can beshaped like a circle or ellipse, and the pumping surface of the solidstate laser chip can have a curvature. In this case, the solid statelaser chip can be pumped with a high degree of efficiency.

Embodiment 2

FIG. 9 is a block diagram showing a main part of a solid state laserpumping module in accordance with embodiment 2. The solid state laserpumping module has the same structure as that of embodiment 1 unlessexplicitly shown otherwise, and offers the same advantages as providedby that of embodiment 1.

A pumping surface, which is a side surface of a solid state laser chip 2and which is a light incidence surface via which pumping light from apumping source is incident the solid state laser chip 2, is not parallelto a direction of the thickness of the solid state laser chip 2, but isinclined with respect to the direction of the thickness of the solidstate laser chip 2. The pumping light 23 enters the interior of thesolid state laser chip 2 via the inclined pumping surface 91. Thepumping source 20 is arranged so as to be inclined toward a directionwhich is the same as that toward which the pumping surface 91 isinclined.

Semiconductor laser light is emitted out of the pumping source with alarge spread angle in a direction of the fast axis of the pumpingsource. However, the semiconductor laser light has components whichtravel in straight lines without spreading at all. In a case where thesolid state laser chip has a pumping surface 9 which is parallel to adirection of the thickness of a solid state laser medium 3 and pumpinglight is incident upon a part of the pumping surface 9 which is a partof a side surface of a non-doped medium 4, since components of thepumping light which travel in straight lines are not reflected by theupper and lower surfaces of the solid state laser chip, they propagatethe interior of the solid state laser chip 2 and outgo from a surfacewhich is opposite to the pumping surface 9 without being absorbed by thethin solid state laser medium 3. In contrast, in the solid state laserpumping module 1 in accordance with this embodiment, since the sidesurface which is the light incidence surface via which the pumping light23 is incident upon the solid state laser chip is not parallel to thedirection of the thickness of the solid state laser chip, but isinclined with respect to the direction of the thickness of the solidstate laser chip, and the pumping source 20 is also inclined toward adirection which is the same as that toward which the pumping surface 91is inclined, all components of the pumping light 23 emitted out of thepumping source 20 including components which spread at large angles inthe direction of the fast axis of the pumping source, components whichspread at small angles in the direction of the fast axis of the pumpingsource, and components which travel in straight lines do not travel instraight lines parallel to the upper and lower surfaces of the solidstate laser chip 2 within the solid state laser chip 2. Therefore, everycomponent of the pumping light with any spread angle passes through thethin solid state laser medium 3 and is absorbed by the thin solid statelaser medium 3 while being total-reflected by the upper and lowersurfaces of the solid state laser chip and therefore traveling along abent optical path. For example, when the inclined pumping surface 91 isinclined at an angle of 30 degrees with respect to the direction of thethickness of the solid state laser medium 3 and the pumping source 20 isalso inclined at the same angle toward the same direction, all thecomponents including components which emit from a semiconductor laserbar 22 and travel in straight lines are not parallel to the upper andlower sides surface of the solid state laser chip 2 within the solidstate laser chip 2 even if the pumping light 23 emitted out of thesemiconductor laser bar 22 has a spread angle of ±45 degrees in thedirection of the fast axis of the semiconductor laser bar 22. Forexample, in a case where YAG is used as the non-doped medium and thebase material of the solid state laser medium 3 is also YAG, everycomponent of the pumping light having any spread angle satisfies totalreflection conditions at the upper and lower surfaces of the solid statelaser chip 2 and therefore can propagate through the solid state laserchip 2 while being reflected zigzag between the upper and lower surfacesof the solid state laser chip 2 even when the pumping light has a spreadangle of ±45 degrees in the direction of the fast axis of the pumpinglight source. Therefore, since the thin solid state laser medium 3 canabsorb every component having any spread angle, the thin solid statelaser medium 3 can be pumped with a high degree of efficiency. As aresult, the present embodiment offers an advantage of being able toprovide high-power laser light with a high degree of efficiency.

Embodiment 3

FIG. 10 and 11 are block diagrams showing a solid state laser chip of asolid state laser pumping module in accordance with embodiment 3. FIG.10 is a cross-sectional view taken along the line B-B of FIG. 11, andFIG. 11 is a cross-sectional view taken along the line A-A of FIG. 10.The solid state laser pumping module has the same structure as that ofembodiment 1 or 2 unless explicitly shown otherwise, and offers the sameadvantages as provided by those of embodiments 1 and 2.

In accordance with the above-mentioned embodiments, the thin solid statelaser medium 3 is shaped like a square or rectangle in cross section.The thin solid state laser medium 3 can have such an arbitrary shape asa hexagon, octagon, circle, or ellipse, in cross section. On the otherhand, the solid state laser chip 2 needs to have a pumping surface 9which is a plane surface because it is pumped by, for example, abar-shaped semiconductor laser. For this reason, a thin solid statelaser medium composite material 10 can be used instead of using thesingle thin solid state laser medium 3 of the above-mentionedembodiments. The thin solid state laser medium composite material 10 iscomprised of a thin solid state laser medium 3 and second non-dopedmedia 11. The second non-doped media 11 having the same thickness as thethin solid state laser medium 3, and are arranged around the perimeterof the thin solid state laser medium 3. The thin solid state lasermedium 3 and the second non-doped media 11 are bonded to each other attheir boundary surfaces parallel to a direction of the thickness of thethin solid state laser medium 3 using a diffusion bonding technique,optical contact technique, or a technique for manufacturing ceramics,and the boundary surfaces have a very small optical loss. Since thesecond non-doped media 11 are arranged around the perimeter of the thinsolid state laser medium 3 having an arbitrary shape, the thin solidstate laser medium composite material 10 can be formed so as to havelateral plane side surfaces regardless of the shape of the thin solidstate laser medium 3 by making the shapes of the second non-doped media11 match with that of the thin solid state laser medium 3. Therefore,the solid state laser chip can be pumped by pumping light from thebar-shaped semiconductor laser which is incident thereupon via twopumping surfaces 9 which are lateral-side surfaces of the thin solidstate laser medium composite material in the direction of the thicknessof the thin solid state laser medium composite material. The thin solidstate laser medium composite material 10 is bonded to a non-doped medium4 over the whole of an upper surface thereof. The thin solid state lasermedium composite material 10 and the non-doped medium 4 are bonded toeach other using a bonding technique, such as a diffusion bondingtechnique, an optical contact technique, or a technique of manufacturingceramics, as in the case of bonding the solid state laser medium 3 andthe non-doped medium 4 to each other. Therefore, boundary surfaces ofthe thin solid state laser medium composite material 10 and thenon-doped medium 4 have a very small optical loss. In the solid statelaser chip 2, the thin solid state laser medium composite material 10and the non-doped medium 4 are bonded to each other over the whole oftheir boundary surfaces, and a reflecting coating 6 for reflecting lighthaving the same wavelength as laser light to be pumped is formed on alower surface of the thin solid state laser medium composite material 10which is opposite to the boundary surface of the thin solid state lasermedium composite material 10 to which the non-doped medium 4 is bonded.

An example of the thin solid state laser medium composite material 10 isshown in FIG. 10. In this example, the solid state laser medium 3 has acircular shape. As an alternative, the solid state laser medium 3 canhave a polygonal or elliptic shape. FIG. 11 shows a side view of thesolid state laser chip 2 which employs the thin solid state laser mediumcomposite material 10. The boundary surface of the thin solid statelaser medium composite material 10 which is bonded to the non-dopedmedium 4 has a rectangular shape. In this cross section, the thin solidstate laser medium 3 included in the thin solid state laser mediumcomposite material 10 has a circular shape, the second non-doped media11 are surrounded by the circular thin solid state laser medium 3, andthe thin solid state laser medium composite material 10 has arectangular shape. The rectangular thin solid state laser mediumcomposite material 10 and the non-doped medium 4 having the same shapeas the thin solid state laser medium composite material 10 are bonded toeach other over the whole of their boundary surfaces, and the reflectingcoating 6 for reflecting light having the same wavelength as laser lightto be pumped is formed on the lower surface of the thin solid statelaser medium composite material 10 which is opposite to the boundarysurface of the thin solid state laser medium composite material 10 towhich the non-doped medium 4 is bonded. Lateral side surfaces of thesolid state laser chip 2 which is thus constructed serve as the pumpingsurfaces 9. Since the solid state laser chip 2 is constituted asmentioned above, it has a circular gain region. Therefore, when carryingout laser oscillation, the solid state laser chip can provide outputlaser light 3 having a concentric circular shape without having to use aspecial measure for arranging a circular aperture in the laser cavitythereof so as to shape the output laser light into a circle in crosssection. If the solid state laser chip has a rectangular gain region andprovides circular output laser light, since energy is extracted onlyfrom a part of the thin solid state laser medium in which the circularlaser light and the gain region overlap each other, the rectangular gainregion has a portion from which energy cannot be extracted even thoughpumped by the pumping light. As a result, the efficiency of extractionof energy may be reduced in this case. In contrast, since the thin solidstate laser medium 3 in accordance with this embodiment can have acircular shape and hence a circular gain region, the percentage by whichthe circular laser beam and the gain region overlap each other is highand therefore a high degree of efficiency of extraction of energy isobtained. Therefore, the present embodiment offers an advantage of beingable to provide high-power laser light with a high degree of efficiency.

INDUSTRIAL APPLICABILITY

As mentioned above, the solid state laser pumping module in accordancewith the present invention can be applied to a laser oscillator or alaser amplifier, and is suitable for providing high-power laser lightwith a high degree of efficiency.

1. A solid state laser pumping module including a plate-shaped thinsolid state laser medium, a reflecting means formed on a plane surfaceof said thin solid state laser medium, a cooling means bonded to saidreflecting means, a pumping source for providing pumping light to saidthin solid state laser medium, laser light being incident upon a laserlight incidence surface which is opposite to said reflecting means,characterized in that said thin solid state laser medium is a platewhose at least a part on a side of said reflecting means has an activematerial doped thereinto, a plate-shaped non-doped medium is disposed onanother plane surface of said thin solid state laser medium which isopposite to said plane surface of said thin solid state laser medium onwhich said reflecting means is disposed, and said two plates areoptically bonded to each other.
 2. The solid state laser pumping moduleaccording to claim 1, characterized in that said module has a pumpingsurface via which the pumping light is introduced into a side surface ofsaid plate-shaped thin solid state laser medium, and said pumping lightpropagates through said thin solid state laser medium and pumps saidthin solid state laser medium while being reflected between saidreflecting means disposed on said thin solid state laser medium and saidlaser light incidence surface.
 3. The solid state laser pumping moduleaccording to claim 2, characterized in that said pumping surface isformed at a certain angle with respect to a direction of normal to saidreflecting means, and the pumping light emitted out of said pumpingsource has an optical axis which is substantially parallel to the normalto said pumping surface.
 4. The solid state laser pumping moduleaccording to claim 2, characterized in that either of diffusion bonding,optical contact, and a ceramic manufacturing means is used as a meansfor bonding the plate whose at least a part on a side of said reflectingmeans has an active material doped thereinto to the plate-shapednon-doped medium disposed on the other plane surface of said thin solidstate laser medium which is opposite to said plane surface of said thinsolid state laser medium on which said reflecting means is formed. 5.The solid state laser pumping module according to claim 1, characterizedin that the plane surfaces of said thin solid state laser medium areinclined with respect to each other.
 6. The solid state laser pumpingmodule according to claim 2, characterized in that a plurality of saidpumping surfaces are arranged on a side surface of said thin solid statelaser medium, and a plurality of pumping sources for outputting pumpinglight to said plurality of pumping surfaces, respectively are arranged.7. The solid state laser pumping module according to claim 1,characterized in that said active material of said thin solid statelaser medium is Yb.